The present invention relates to the chemical vapor infiltration techniques used in particular when making parts out of thermostructural composite material. The invention relates more particularly to chemical vapor infiltration of porous substrates of complex three-dimensional shapes such as fiber preforms for use in fabricating aeroengine blades.
In order to fabricate parts out of composite material, in particular parts made of thermostructural composite material constituted by a preform made of refractory fibers (e.g. carbon fibers or ceramic fibers) densified by a refractory matrix (e.g. of carbon and/or ceramic), it is common practice to make use of infiltration methods. Examples of such parts are: thruster nozzles made of carbon-carbon (C—C) composite; brake disks, in particular for airplane brakes, made of C—C composites; and blades made of ceramic matrix composite (CMC). Likewise, before, during, or after densification of preforms, one or more layers, e.g. of interphase material, may be deposited in the preforms, likewise by using the chemical vapor infiltration technique.
Chemical vapor infiltration consists in placing the substrates in a reaction chamber of an infiltration installation with the help of support tooling, and in admitting a reagent gas into the chamber, with one or more constituents of the gas being precursors for the material that is to be deposited within the substrates in order to densify them and/or in order to deposit a layer, e.g. of interphase material. Infiltration conditions, in particular concerning the composition and the flow rate of the reagent gas, and also the temperature and pressure inside the chamber, are selected so as to enable the gas to diffuse within the accessible internal pores of the substrates in order to cause the desired material to be deposited therein by decomposing a constituent of the gas or by a reaction between a plurality of constituents of the gas. The reagent gas is conventionally pre-heated by passing the gas through a preheater zone situated in the reaction chamber, and into which the reagent gas inlet opens out. That method corresponds to the free flow chemical vapor infiltration method.
In an industrial chemical vapor infiltration installation, it is common practice to load the reaction chamber with a plurality of substrates or preforms for densifying simultaneously in order to increase the throughput of the densification method, and consequently in order to increase the loading factor of the reaction chambers.
Methods and installations for chemical vapor infiltration of porous annular substrates are described in particular in documents US 2004/237898 and U.S. Pat. No. 5,904,957. Nevertheless, those methods apply essentially to infiltrating substrates of annular shape that are arranged in stacks, and they are not adapted to infiltrating substrates that present shapes that are not axisymmetric.
Document US 2008/0152803 describes the use of loader tooling comprising a tubular duct arranged between first and second plates, and around which thin substrates are arranged radially in the form of a plate for densifying. The tooling as loaded in that way is then arranged inside a reaction chamber of an infiltration oven having its reagent gas admission inlet connected to the tubular duct for enabling a reagent gas to be admitted into the duct, which then distributes the gas along the main faces of the substrates in a flow direction that is essentially radial.
Nevertheless, that loader tooling remains limited to directed-flow densification of thin substrates that are simple in shape, such as fine rectangular plates, and it cannot be used for uniform densification of porous substrates presenting complex three-dimensional shapes, such as fiber preforms for blades. Specifically, the flow of a stream of gas over substrates of complex three-dimensional shape is more difficult to control. Likewise, that type of tooling gives rise to thermal dispersion that makes it difficult to obtain easy control over temperature at all points of the preforms and between the preforms. The lack of control over the flow of the reagent gas over all of the preforms that are to be infiltrated gives rise to gradients appearing in densification or deposition within the substrates. However, obtaining uniform densification or deposition within a substrate is essential for the mechanical performance of the resulting part.
Also, the loading factor in infiltration installations using tooling in which the preforms for infiltrating are arranged radially is relatively low. Industrial scale production of parts of complex three-dimensional shape then requires a large number of infiltration installations to be fabricated and used, which is highly penalizing in economic terms.